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Carl Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, cosmologist, astrophysicist, astrobiologist, author, science popularizer, and science communicator in astronomy and other natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. Sagan wrote many popular science books, such as The Dragons of Eden, Broca’s Brain and Pale Blue Dot, and narrated and co-wrote the award-winning 1980 television series Cosmos: A Personal Voyage. The most widely watched series in the history of American public television, Cosmos has been seen by at least 500 million people across 60 different countries. The book Cosmos was published to accompany the series. He also wrote the science fiction novel Contact, the basis for a 1997 film of the same name. His papers, containing 595,000 items, are archived at The Library of Congress.

Sagan always advocated scientific skeptical inquiry and the scientific method, pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI). He spent most of his career as a professor of astronomy at Cornell University, where he directed the Laboratory for Planetary Studies. Sagan and his works received numerous awards and honors, including the NASA Distinguished Public Service Medal, the National Academy of Sciences Public Welfare Medal, the Pulitzer Prize for General Non-Fiction for his book The Dragons of Eden, and, regarding Cosmos: A Personal Voyage, two Emmy Awards, the Peabody Award and the Hugo Award.

Sagan was the David Duncan Professor of Astronomy and Space Sciences and Director of the Laboratory for Planetary Studies at Cornell University. He played a leading role in the American space program since its inception. He was a consultant and adviser to NASA since the 1950’s, briefed the Apollo astronauts before their flights to the Moon, and was an experimenter on theMariner, Viking, Voyager, and Galileoexpeditions to the planets. He helped solve the mysteries of the high temperatures of Venus (answer: massive greenhouse effect), the seasonal changes on Mars (answer: windblown dust), and the reddish haze of Titan (answer: complex organic molecules).

For his work, Dr. Sagan received the NASA medals for Exceptional Scientific Achievement and (twice) for Distinguished Public Service, as well as the NASA ApolloAchievement Award. Asteroid 2709 Sagan is named after him. He was also awarded the John F. Kennedy Astronautics Award of the American Astronautical Society, the Explorers Club 75th Anniversary Award, the Konstantin Tsiolkovsky Medal of the Soviet Cosmonauts Federation, and the Masursky Award of the American Astronomical Society, (“for his extraordinary contributions to the development of planetary science…As a scientist trained in both astronomy and biology, Dr. Sagan has made seminal contributions to the study of planetary atmospheres, planetary surfaces, the history of the Earth, and exobiology. Many of the most productive planetary scientists working today are his present and former students and associates”).

He was also a recipient of the Public Welfare Medal, the highest award of the National Academy of Sciences (for “distinguished contributions in the application of science to the public welfare…Carl Sagan has been enormously successful in communicating the wonder and importance of science. His ability to capture the imagination of millions and to explain difficult concepts in understandable terms is a magnificent achievement”).

Dr. Sagan was elected Chairman of the Division of Planetary Sciences of the American Astronomical Society, President of the Planetology Section of the American Geophysical Union, and Chairman of the Astronomy Section of the American Association for the Advancement of Science. For twelve years he was the editor-in-chief of Icarus, the leading professional journal devoted to planetary research. He was cofounder and President of the Planetary Society, a 100,000-member organization that is the largest space-interest group in the world; and Distinguished Visiting Scientist, Jet Propulsion Laboratory, California Institute of Technology.

A Pulitzer Prize winner for the book The Dragons of Eden: Speculations of the Evolution of Human Intelligence, Dr. Sagan was the author of many bestsellers, including Cosmos, which became the bestselling science book ever published in English. The accompanying Emmy and Peabody award-winning television series has been seen by a billion people in sixty countries. He received twenty-two honorary degrees from American colleges and universities for his contributions to science, literature, education, and the preservation of the environment, and many awards for his work on the long-term consequences of nuclear war and reversing the nuclear arms race. His novel, Contact, is now a major motion picture.

In their posthumous award to Dr. Sagan of their highest honor, the National Science Foundation declared that his “research transformed planetary science… his gifts to mankind were infinite.”

Dr. Sagan’s surviving family includes his wife and collaborator of twenty years, Ann Druyan; his children, Dorion, Jeremy, Nicholas, Sasha, and Sam; and grandchildren.

Carl Sagan’s Vision of Mars

Visions of Mars is a message from our world to future human inhabitants of Mars, which launched on its way to the Red Planet in 2007 aboard the spacecraft Phoenix. Along with personal messages from leading space visionaries of our time, the message will include a priceless collection of Mars literature and art, and a list of hundreds of thousands of names of space enthusiasts from around the world. The entire collection will be encoded on a mini-DVD provided by The Planetary Society, which will be affixed to the spacecraft.

Carl Sagan recorded a message to the future Martians from near his home in Ithaca, New York, with a water fall cascading in the background. You can listen to it here.

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Launched by NASA on September 5, 1977, to study the outer solar system, the Voyager 1 is the furthest human-made object from Earth. As of January 10, 2019, the space probe is more than 13,491,481,615 miles (21,712,434,988 km) away from our home planet. It is also moving away at a speed of 38,026.77 mph (61,198.15 km/h) relative to the Sun. But, thanks to NASA’s Deep Space Network (DSN) Notes 1, we can still communicate with it (also with its sister, Voyager 2). But how far can Voyager 1 go before we lose communication?

The video published by the Primal Space channel below looks at how we communicate with Voyager and when it will eventually stop receiving our signals.

Currently, we’re slowly transitioning to renewables and fusion energy may become available in the future. If we don’t destroy ourselves or the environment, as humanity progress further, we will likely gain complete control of the Earth’s resources. At that stage, we’ll probably begin to look outwards for new places to expand into. But, if we want to expand into outer space someday, our planet’s resources are not enough (see the Kardashev scale below). We’d need incredible amounts of energy, even to expand into our solar system. Luckily, we know where to find it: the Sun. To harvest energy from the Sun, we can build a megastructure called “Dyson Sphere” around it and capture a large percentage of its power output.

Back in December 1990, during its flyby of Earth, NASA’s Galileo spacecraft, which studied the planet Jupiter and its moons, as well as several other Solar System bodies, pointed its instruments towards Earth, at the urging of Carl Sagan. And, it has found evidence of life on our planet. This can be a key to detect vegetation on exoplanets – which is a key to a possible intelligent extraterrestrial life.

In a paper published on Nature, researchers wrote “The Galileo spacecraft found evidence of abundant gaseous oxygen, a widely distributed surface pigment with a sharp absorption edge in the red part of the visible spectrum, and atmospheric methane in extreme thermodynamic disequilibrium. Together, these are strongly suggestive of life on Earth.”

NASA’s asteroid-sampling OSIRIS-REx spacecraft captured a new Earth-Moon image on Jan. 17, 2018, from a distance of 39.5 million miles (63.6 million kilometers). Spacecraft used its NavCam1 imager to take this photo, as part of an engineering test. In the image, The Earth and the moon are just two bright dots against the vastness of black space – which reminds us of Carl Sagan’s famous speech: “That’s here. That’s home. That’s us.”

It took 27 years, but finally, NASA’s New Horizons spacecraft beat Voyager 1’s record for being farthest from Earth while capturing images. Taken on December 5, 2017, New Horizons image of the open star cluster NGC 3532 (also commonly known as the Football Cluster or the Wishing Well Cluster) became the farthest image ever made by any spacecraft, breaking a 27-year record set by Voyager 1. But for a very short time! About 2 hours later, New Horizons broke its own record with images of two Kuiper Belt objects.

For a short time, the image below, New Horizons Long Range Reconnaissance Imager (LORRI) frame of the galactic open star cluster NGC 3532 (aka the Football Cluster or the Wishing Well Cluster), taken on December 5, 2017 (released on February 8, 2015), was the farthest image ever made by a spacecraft, breaking a 27-year record set by Voyager 1. New Horizons was 3.79 billion miles (6.12 billion kilometers or 40.9 astronomical units-AUNotes 1) from Earth when LORRI took the routine calibration image.

Earth is actually a fragile and isolated rock, a “blue marble” in a vast, cold and hostile space. But only after seeing our planet from space we truly understood that. Seeing the Earth first time from a distance was a powerful experience which has changed the way we see our planet. Here are the top 10 most iconic photos of Earth from space.

Carl Sagan’s famous quote says “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” In that famous quote, Sagan makes reference to the whole universe started off with hydrogen and helium, all stars produce helium, and then stars over a certain mass threshold produce carbon, nitrogen, oxygen and lots of heavier elements – which are also the source of the life. The star stuff is inside us – every living thing on Earth.

But, even stars aren’t powerful enough to create heavy elements like silver, gold, and cesium. Since the 1950s, scientists have wondered: where do most of the elements in the periodic table come from?

Eratosthenes knew that at local noon on the summer solstice (at the time of the longest day, about 21 June in the northern hemisphere) in Syene (modern Aswan, Egypt), the Sun was directly overhead – Syene was in fact slightly north of the tropic, though (1). Local noon is – technically when the sub-solar point is somewhere over your meridian, it’s noon for you. So, on that day, Syene is the sub-solar point of Earth (the sub-solar point on a planet is where its sun is perceived to be directly overhead). To learn more about the local noon and the subsolar point, see the article titled “How Earth Moves“.

The Earth is our one and only home. As Carl Sagan said (Pale Blue Dot: A Vision of the Human Future in Space), “On Earth, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.”.

But will we ever leave our home and visit other stars in the future?

Our galaxy, “The Milky Way” is a barred spiral galaxy (a spiral galaxy with a central bar-shaped structure composed of stars) some 100,000-120,000 light-years in diameter, which contains 100-400 billion stars. It may contain at least as many planets as well. Our Sun (the Solar System) is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm.